The present invention relates to a projection tube wherein video images are produced, and a video projection system whereby the video images produced by the foregoing projection tube are enlarged and projected.
A prior art projection tube for video projection systems will be explained with the help of FIG. 9.
FIG. 9 is a cross-sectional view to show structures of a main part of a prior art projection tube for video projection systems.
A cathode ray tube 21 and a projection lens 22 are put together by means of a radiator 24 (functioning as a vessel to hold a solution as well), and a solution 23 is filled in the radiator 24.
The junction between the cathode Pay tube 21 and the radiator 24 is mechanically sealed by a uniform thickness sealing member 27 having a flange of a uniform thickness.
The junction between the projection lens 22 and the radiator 24 is mechanically sealed by a sealing member 25.
The angle between the face plane of the cathode ray tube 21 and the projection lens 22 [(W), referred to as "slant angle" hereafter] is adjusted to a required angle by controlling the shape of the radiator 24.
More specifically, the slant angle (W) is controlled by making the height of the respective side walls of the radiator 24 differ from one another to give a different shape to the radiator 24 as a whole, resulting in providing a slant to the radiator 24. Thus, a complete projection tube is structured.
Three projection tubes, i.e. a red color projection tube, a green color projection tube and a blue color projection tube, are arranged, and a screen (not shown in FIG. 9) is disposed in front of the projection tubes, to build a complete video projection system.
In the foregoing set-up, the video images produced on the face plane of the cathode ray tube 21 are enlarged and projected on the screen by the projection lens 22. At this time, the slant angle (W) of each respective projection tube, i.e. the red color, green co)or and blue color projection tubes, is adjusted to an angle different from one another in order to have the positions of the video images from each respective projection tube coincided with one another.
The solution 23 serves the functions of cooling off the heat generated by the cathode ray tube 21 and also enhancing the contrast of video images.
With the prior art structures as described above, the establishment of the slant angle (W) was dependent on the shape of the radiator 24, and each respective projection tube for red, green or blue video image projection required a radiator 24 serving as the structural material thereof and having a specific configuration different from that of other projection tubes.
Furthermore, when a video projection system required optical design figures different from those of other video projection systems, a new specific radiator 24 of a different configuration was needed.
All these factors as described in the foregoing brought about the problem of increased expenses involved with metal dies for production.
Besides, the cathode Pay tube 21 made of glass and the radiator 24 made of metal are put together by means of an elastic and uniform thickness sealing member 27 with a flange structure placed in the junction therebetween in order to prevent leakage of solution and breakage of glass. This structure tended to cause an error in setting a slant angle.
Moreover, a position fixing between the cathode ray tube 21 and the radiator 24 was made inaccurately when the both were put together, resulting in an error in axis alignment between the cathode ray tube 21 and the projection tube 22. All of these factors adversely affected the focusing performance of the video images projected on the screen with a resultant problem of deteriorated video image quality.